These experiments are designed to study the re-establishment of connections between two populations of uniquely identifiable cells which are originally connected in a very precise pattern. The superficial flexor muscle of the crayfish Procambarus clarkii is innervated by six axons which make connections with 40-50 muscle fibers in a pattern that depends on the position of the individual muscle fibers on the surface of the muscle. I propose to study the regeneration of neuromuscular connections in this system. Crustacean neurons can regenerate by the fusion of the two cut ends of the axons and by regrowth of the proximal stump, either in the presence of a surviving distal stump or in its absence. The first experiments are designed to obtain these three types of regeneration on the same muscle system, for each one will provide insight into different aspects of the regenerative process. The second series of experiments will analyze the specificity of the regenerated connectivity map. In the third series of experiments the position and orientation of the postsynaptic field will be changes; regeneration will take place in fibers which still have functional synapses. By comparing normal regeneration with the regeneration that occurs under changed conditions, one would be able to study the effect of muscle fiber position or the presence of old terminals on the specificity of the regenerated process. These results will give us an indication of the possible developmental mechanisms that were responsible for the formation of the original specific neuromuscular connections.